1. Field of the Invention
The present invention relates to distribution of solid particles flowing in a fluid, and more particularly to coal particle distribution in airflow through coal piping systems.
2. Description of Related Art
A variety of devices and methods are known in the art for delivering pulverized coal to coal fired burners. Of such devices, many are directed to improving particle distribution within coal piping systems for delivering coal to be combusted.
Coal powered plants require an efficient means of supplying coal as fuel to produce heat power. Raw coal is typically pulverized in a coal pulverizer or mill to produce small coal particles or coal dust. The pulverized coal must then be delivered to a furnace or burner where it can be used for combustion. This is typically done with a coal piping system that utilizes air flows to transport pulverized coal particles from the mill or pulverizer to a nozzle where coal particles are injected into the coal burner or furnace. As the coal particles travel in the air flow through the piping system, bends in the piping and the pipe geometry in general tend to cause non-uniform coal particle distribution. A densely packed region of coal particles extending through a piping system is referred to a coal “rope.”
Coal roping causes various technical problems for operation and maintenance of coal systems. The poor distribution of coal particles can extend into the combustion zone, where localized imbalances in the fuel/air mixture tend to cause inefficient combustion and elevated emissions of NOx, CO, and other pollutants. It can also cause elevated levels of unburned carbon in the fly ash, which will lower combustion efficiency. Also, the highly abrasive nature of the coal rope impacting and scrubbing components of the coal piping and burning system causes extensive erosion of pipes and other components in the system, leading to frequent need for inspection, repairs, and replacement of parts. If inspections, repairs and replacements are not performed in a timely manner, there is an elevated chance that abrasion from coal roping will cause expensive or dangerous failures of key components.
One component that is particularly problematic for coal roping is the dividing head at the junction between a single pipe upstream of two or more branching pipes downstream, as is commonly seen upstream of directional flame burner coal nozzles, for example. In such a dividing head, if a flow with a coal rope enters the dividing head, one of the downstream legs will tend to receive the coal rope portion of the flow, meaning that one of the downstream nozzles will receive significantly more coal than the other nozzle or nozzles connected to the same dividing head.
Such conventional methods and systems have generally been considered satisfactory for their intended purpose. However, there is still a need in the art for systems and methods that allow for improved particle distribution downstream of dividing heads, for example. There also remains a need in the art for such systems and methods that are easy to make and use. The present invention provides solutions for these problems.